System and method of electron beam writing

ABSTRACT

A system and method for improved electron beam writing that is capable of taking design intent, equipment capability and design requirements into consideration. The system and method determines an optimal writing pattern based, at least in part, on the received information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/607,753, filed on Nov. 30, 2006, now issued as U.S. Pat. No.7,777,204, which claims benefit of U.S. Provisional Application No.60/741,696 filed on Dec. 1, 2005, all of which are hereby incorporatedby reference in their entities.

BACKGROUND

Electron Beam Writing (EBW) technology plays an important role in ICfabrication. It is used as a main tool for lithography mask writing.Recently its variation, the Electron Beam Direct Writing (EBDW)technology, has been considered as a prominent candidate for low volumeIC production at 90 nm and below. These approaches have become solutionsthat are used to address mask cost issues for low volume LSI production.

The major weakness of this technology is its relatively low throughput.To overcome this barrier, the Variable Shape Beam (VSB) and the CellProjection (CP, alternatively called Character Projection, or BlockProjection) techniques have been introduced. The cell projectiontechnique uses a stencil that allows writing of complicated repetitivepatterns (CP cells) by one exposure shot, thus decreasing overallexposure time and increasing the writing system throughput. To utilizecapabilities of the CP technique, a stencil design system has to bedeveloped that is capable of proper repetitive pattern extraction, CPcell design and optimum CP cell placement on the stencil.

As shown in FIG. 1, this technique allows writing complicated patternsby one shot with an electron gun 100 that produces an electron beam 102,thus increasing throughput of the system. As noted, a central part ofthe technique is a stencil 110 that consists of a number of stencilpatterns 112, alternatively called characters or CP cells. To increasethe throughput and accuracy of a CP system, proper stencil patterndesign is necessary. This technique produces an image 120 of a selectedstencil pattern 114 on a substrate 122.

Although EBW technology provides many advantages, it is not perfect.Various effects negatively affect the process quality, decreasing yieldand lowering overall throughput. Certain effects like Coulomb blur,proximity effect, electron beam (EB) distortions can be minimized byproper stencil design. Such processing may include, for example, moredetailed fracturing and dose calculation, proper CP cell design andstencil layout. However, such calculations lead to the increase of thedata volume and writing time. Also, making such calculations for thewhole writing pattern is a time and resources consuming task.

As an enhancement of the CP writing technique, there exists the partialexposure method. In this method, a part of a CP cell can be illuminated,allowing writing not only whole CP cell but also its part by one shot.The advantage of this method is that one CP cell can be used for writingdifferent patterns. Therefore, the same stencil can be used for writingmore patterns by one shot.

The conventional partial CP exposure method has disadvantages. To exposea part of a CP cell, there must be a blank region around the cell thatblocks the rest of the beam, as in most EB writing systems, the size ofthe beam illuminating the stencil is fixed by the first aperture. Ifanother CP cell appears in the region that is supposed to be blank, apart of it will be exposed. Therefore, in the conventional partial CPexposure art, the cells are less densely packed than those could bewithout using partial CP exposure, because partial CP cells must haveenough surrounding blank space.

Automation of the data preparation process for EBDW systems is a problemthat has not been satisfactory solved yet. To achieve good throughput,repetitive design patterns must be selected and processed, then placedas CP cells on the stencil. Simultaneously, quality issues must beproperly taken into account to maintain acceptable yield.

In current systems, the above mentioned problems are partially solved byintroducing specific design flows and data processing algorithms foreach specific design. The development of a layout specific stencildesign system significantly increases the overall development time,therefore making the technology less advantageous.

There are also problems related to feature miniaturization insemiconductor devices. With the feature size decrease, writing accuracybecomes more and more important. But required accuracy is not uniformfor all parts of a design. Some parts require tighter tolerances, someparts require less accuracy. The required accuracy depends on thefeature's design intent. Current EBDW systems do not have capabilitiesfor design intent aware operation.

Geometric structure of a CP cell and its position on the stencilstrongly affect writing quality. To achieve required quality andsimultaneously maximize the usage of stencil area, careful CP cellextraction and stencil layout optimization are needed that take thedesign intent information into account. Current data preparation systemsdo not support this functionality.

SUMMARY

The invention provides an improved approach by using design intentinformation during the data preparation process To make an optimizedstencil design, to automate the data preparation, and to maintain themoderate complexity of the system, design intent information can beintroduced during the data preparation process. The design intentinformation is particularly used in the stencil design phase, by takingmore care to more critical part of the layout and locally balancingbetween accuracy and speed. To achieve this, some embodiments of theinvention use design intent information in addition to the originaldesign data. The design intent information may be, for example, in theform of numbers representing criticality of portions of the layout. Whendesign intent is known, different processing rules can be associatedwith different intent categories. This additional processing informationis also supplied to the data preparation system. For example, portion ofthe layout having higher criticality level can be processed moreaccurately than less critical parts. This allows designing more optimalstencil. Therefore, system accuracy and throughput are balanced moreoptimally.

The present invention provides an approach which avoids the problemswith conventional approaches described in the background section. Inparticular, it is noted that a conventional stencil may already havecells with large blank adjacent regions. Those cells are the cells thatare surrounded by the blank region being used for VSB exposure. However,the conventional method that uses the blank region consumes expensivestencil area. By this invention the periphery of the stencil (indicatedas space between apertures in FIG. 10) is used for the blank region andsaves waste of the stencil area. As beam distortions are higher on theperiphery, the periphery cells can be used as partial CP cells fornon-critical parts of the layout, while those cells that are surroundedby the blank area in the center of the stencil (this blank area is usedfor VSB writing) can be used as partial CP cells for critical parts ofthe layout.

In one embodiment, a method of electron beam writing includes receivingand combining stencil design data, design intent data and equipmentcapability data. An optimal electron beam writing pattern is determinedbased, at least in part, on the combined stencil data, design intentdata and equipment capability data. An electron beam is directed inaccordance with the optimal electron beam writing pattern.

In another embodiment, a method for electron beam writing includesaccessing input data or information, statistically analyzing a celllayout pattern by calculating a number of repetitions of at least onecell of the cell layout pattern, and building cell projection candidatesby analyzing statistical information of the repetitive portions of thecell layout pattern. The method includes placing the cell projectioncandidates on a stencil, estimating throughput of the cell projectioncandidates, and generating a stencil table.

In one aspect, accessing input data or information includes accessing atleast one of design intent data, stencil data and equipment capabilitydata, and/or accessing the input data or information includes at leastone of assigning criticality levels to various portions of the designand defining geometric tolerances to classes of geometric shapes.Statistically analyzing a cell layout pattern includes determining thenumber of electron beam shots required to write the cell layout pattern.Building cell projection candidates includes conforming repetitiveportions of the cell layout pattern to one or more stencil design rules.The one or more stencil design rules include at least one of maximalsize of cell, absence of forbidden patterns including donut shapes andcantilevers, shape density and shape size constraints.

In another aspect, conforming repetitive portions of the cell layoutpattern to one or more stencil design rules includes modifying the celllayout pattern to conform to the one or more stencil rules. Estimatingthroughput of the cell projection candidates includes comparing thecalculated estimate against one or more corresponding targets.Estimating throughput of the cell projection candidates includesdetermining whether one or more predefined rules or conditions aresatisfied. Generating the stencil table includes taping out the stencildata.

In still another embodiment, a stencil design system for electron beamwriting includes at least one database for storing design intent dataand stencil design rules, an electron beam writer, and a processor forreceiving design intent data and stencil design rules from the at leastone database and for generating a cell table for the electron beamwriter.

These and other objects and advantages of the present teachings willbecome more fully apparent from the following description taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example electron beam writing technique.

FIG. 2 depicts and embodiment of a system for electron beam writing.

FIG. 3 depicts an embodiment of a method for electron beam writing.

FIGS. 4-11 provide illustrative examples of approaches to implementssteps in the flowchart of FIG. 3.

FIG. 12 depicts a computerized system on which a method for electronbeam writing can be implemented.

DETAILED DESCRIPTION

Reference will now be made to the drawings wherein like numerals referto like parts throughout.

Some embodiments of the invention provides an improved approach by usingdesign intent information during the data preparation process. Thisprovides many advantages, including an optimized stencil design, permitsautomated data preparation, and allows the method and system to maintainthe moderate complexity of the system. In one embodiment, the system canuse a special processing rule set that allows processing of differentdesign categories, as defined by their design intent, in a differentmanner. This approach is universal and allows balancing of thethroughput and quality in an optimal way. One goal of the invention isto provide a formal way for the data processing that is capable ofaddressing the throughput and quality issues in an optimized way.

FIG. 2 illustrates the structure of the stencil design system 200according to an embodiment of the invention. The initial inputs for thesystem 200 are a design file 202, design library 204, design intent 206that is generally provided for both the design and the library, designintent aware processing rules and constraints (like stencil designrules) 208, and output targets 210. In one aspect, an output of thesystem 200 is a cell table 212 comprising, for example, information onCP cells relevant to the writing process, layout file in a formatreadable by the writing machine, and a stencil layout file 214.

In general, the design data 202 can be represented in any industrialstandard format like GDSII, Open Access, OASIS, or and other knownand/or convenient format. The layout that is a part of the design can bedescribed in terms of geometric shapes (polygons, paths, etc) and/or anyother convenient terms.

The design intent information 206 is used during the data preparation tocategorize layout elements or groups of elements with respect to variousparameters like timing, geometric tolerances, yield and/or any otherconvenient data.

Some data representation standards may not have capabilities to includesuch information in the data file. In this case, the Design Intentinformation can be supplied in the form of a file, or a script, and/orany other convenient manner. The Design Intent can also be included inthe design if the standard input supports necessary syntax.

The design library 204 can include groups of geometric elements that areparts of the layout. In many cases, such groups are related to standardcells. However, in alternate embodiments, other forms are also possible.A memory module and an arithmetic module are examples of different usesof a library. A module compiler uses such groups as components of thetarget module. In the conventional art, the design intent information isnot provided for elements of a design library. However, having designintent information for library elements can be important for optimalstencil design.

The processing rules 208 define what kind of data processing can be donefor each design intent category. For example, fine border fracturing canbe used for shapes with critical geometry, while faster and coarsefracturing can be done for non-critical shapes. As another example, insome embodiments the separation of critical shapes when possible can beavoided, because it can lead to critical dimension violations due toimperfect stitching.

The stencil design rules, an example of constraints 208, describecurrently available stencil manufacturing technologies. Otherconstraints such as precision requirements can also be imposed andincluded as a part of the system's input. To achieve optimal balancebetween quality and speed, the constraints in general can be differentfor different design intent categories. For example, loose constraintscan be set for less critical design constituents, tight constraints canbe assigned to more critical ones.

In some embodiments, the cell table 212 may comprise information that isused by writing system 220 during the writing process. Detailedinformation on stencil design, such as positions of CP cells on thestencil, geometric information of each CP cell, and other relevantinformation, can be contained in the table 212.

The output targets 210 define the structure of desired output, e.g.,throughput requirements etc.

Stencil layout data 214 can describe the geometry of the stencil. Inmany cases, stencil layout 14 can be provided as a file in a standardformat such as GDSII. This file can be transferred to the mask shop 222and used for stencil fabrication. In one aspect, the fabricated stencilcan be used by EBW machine 220.

In some embodiments, the data preparation and stencil design system canmake use of the design intent information to optimally balance thethroughput and quality.

One target of a stencil design system according to some embodiments isto design an optimal stencil for a writing system based on a given inputdata. This provides maximization of throughput of the system andsimultaneously maintaining required writing quality.

FIG. 3 illustrates more details of the operation of the stencil designsystem 200 according to an embodiment of the invention. In one aspect,each of the steps in FIG. 3 are described in greater detail hereinbelow.

At step 1 (302), input data is accessed. In one aspect, the designintent information is either integrated with the design data, or readfrom a separate file, or extracted by running a script with suitablescript processing software.

The design intent information can be represented in various forms.Examples include, but are not limited to, assigning various criticalitylevels to various portions of the design, or defining specific geometrictolerances to certain class of geometric shapes.

At step 2 (304), statistical analysis of the layout is performed. In thecase where the layout has the hierarchical “cell-instance” structure,the number of repetitions of each cell that constitutes layout iscalculated. In the case where the layout data is flat, repetitivepattern extraction (automatic or manual) is performed first, and therepetition number calculation is made for the extracted patterns. It isalso possible to build a new hierarchical structure that betterrepresents repeatability of layout patterns. Also, the number of EBshots required to write the layout, as well as the number of shots foreach cell (or extracted pattern) is estimated.

Patterns that have equal geometry but different design intent may betreated as different during this step. By doing that, more accuratestatistics can be extracted, as in general design elements withdifferent intent should be processed in different manner.

At step 3 (306), statistical information about the repetitive parts ofthe layout collected during step 2 (304) is used for building CP cellcandidates. Since extracted repetitive patterns will be processed forplacing on stencil, these will be configured to obey stencil designrules. In one aspect, the rules include, but are not limited to, maximalsize of a cell, absence of forbidden patterns, such as, for example,doughnut shapes, cantilevers, etc., shape density and shape sizeconstraints. To fulfill these constraints, pattern modification is oftenused.

Pattern modification may be performed at step 3 (306). A CP cellcandidate is checked against the design rules. If a rule is violated,the rule specific action is performed. The goal of this step is not onlyto satisfy stencil design rules, but also to design a CP cell that willbe written with required quality.

During step 3 (306), CP cells candidates are built. Simultaneously, inone aspect, design intent of various features is processed in pertinentmanner; therefore additional requirement such as quality can be takeninto account.

Illustrated examples of specific methods to achieve the goal of step 3(306) will be described in more detail further below in this document.

In step 4 (308), extracted CP cells are placed on a stencil. In manycases, the number of CP cell candidates exceeds the number of CP cellsthat can be placed on a stencil. The present method uses design intentinformation during the CP cell placement phase to built an optimalstencil. Illustrated examples of specific methods to achieve the goal ofstep 4 (308) will be described in more detail further below in thisdocument.

At step 5 (310), the estimation function is calculated. Throughput isone of the most important parameters to estimate, but other parameterscan be taken into account by the corresponding choice of the estimationfunction. Also, multiple functions can be calculated to enhance theestimation.

Due to limitations of the technology and to additional constraints thatmay be imposed, in general it is difficult to write a whole layout bythe CP method only. In a rule, there remains a part of the layout thathas to be written by the VSB method. To estimate the throughput based onCP cells geometry extracted during step 4 (308), preliminary shapefracturing of the remaining part is performed.

Although optimized fracturing can be done after CP cell extraction isfinalized, accurate fracturing estimation is needed for good shot numberand throughput estimation. The estimation step uses design intentinformation to obtain an accurate shot number estimate.

An example of a specific method to achieve the goal of step 5 (310) willbe described in greater detail herein below.

In step 6 (312), the values calculated in step 5 (310) are checkedagainst corresponding targets. The main target for a CP system isthroughput, but other targets also can be taken into account. If thetargets are achieved, the system proceeds to the next step. If not, thesystem returns to the candidates extraction step.

During step 7 (314), the stencil data is checked to determine whetherthe predefined rules and conditions are satisfied. If not all the rulesand conditions are satisfied, then the system proceeds to the correctionflow. If the rules and conditions are satisfied, the system proceeds tostep 8 (316). In one embodiment, during step 8 (316), the Cell Table isprepared and the stencil data is taped out.

There exist design specific algorithms that optimize quality during theextraction process. For example, there are algorithms for extracting CPcells from memory cells that optimize quality as well using specificmemory cell structures and therefore not applicable if a cell candidatedoes not have such structure. In contrast, the present approach does notrequire such specific knowledge about the design. Instead, it usesabstract design categories that can be attached to virtually any designduring the development phase. It also uses processing rules that aredesign intent specific (not layout specific as in conventional art).Therefore, same rules can be used without modifications for same intentcategories, eliminating the need for the re-development of such rulesfor every specific layout.

Illustrative Examples for Step 3

A method of achieving the goal of step 3 (306) according to someembodiments will be described and illustrated by considering thefollowing examples.

EXAMPLE 1

Consider if the size of a CP cell candidate exceeds the maximum allowedsize. In this case, cell separation may be required. In one approach,the separation is done straightforwardly by merely cutting the pattern.In some approaches, a pattern specific algorithm is then applied tomodify the cut patterns to avoid quality problems that are likely toarise when using the straightforward approach. Using such patternspecific algorithms leads to a highly design specific system that has tobe modified if one is going to use it for another design. In contrast tothese schemes, an embodiment of the present approach uses design intentspecific algorithms, instead of an design specific approach, to extractCP cells from a given candidate.

The main issue is that the cutting step can lead to separating criticalshapes. When a shape is separated, it is written in two or more EBshots. Errors during the image stitching and other processimperfections, as well as effects due to processing like difference inexposure doses for the parts of the shape, can lead to imagedistortions, as illustrated in FIG. 4. Such distortions, in turn, ifoccurred in certain parts of the design, can lead to a failed product.Therefore, it is important to process such shapes in accordance to thatspecific role.

To such parts of the design, a corresponding design intent category maybe attached beforehand. For each part of the candidate, the systemselects and applies processing rules from the processing rules set (thatis also designed beforehand and supplied to the system as an input)relevant to this intent category. For example, the processing rules arebuilt in such way that the cutting line avoids certain category ofshapes.

If it is impossible to draw such a line, it usually means that theseshapes cannot be placed in a CP cell and will be written by VSB. Thefracturing rules for VSB writing also use the shape's design intent toperform pertinent operations. For example, if the shape's intent assumestight geometric tolerances, the shape's boundary must be fracturedseparately and dose calculations must be performed accordingly tominimize proximity and Coulomb effects.

EXAMPLE 2

Consider if the extracted candidate contains a doughnut pattern. Mostexisting stencil manufacturing technologies do not allow such patterns,as no mechanical support can be provided for the inner part of theshape. Therefore, such shapes must be separated in two shapes or more.

An example of such pattern is given in FIG. 5. The quality issues arisewhen the shape contains critical regions, as illustrated in the example.If the shape cut by line 1, the critical parts are cut. This canpotentially lead to the same quality issues as described in Example 1.However, such situation can be avoided applying the previously describedstrategy. Namely, if the design intents of some parts of the shape aredifferent, different intent categories are attached, and the parts areprocessed according to these categories. If however the design intent ofthe whole shape is same and the corresponding category does not allowshape separation, the whole shape must be written by VSB method. In thelatter case, fracturing rules pertinent to the intent category apply.

EXAMPLE 3

In this example, it is assumed that during EB writing process, shapeswith different geometries are subject to different distortions. Forexample, Coulomb effect is more severe for wide, thick shapes, whilesmall, thin shapes are less affected. If a critical shape contains boththin and thick parts, as illustrated in FIG. 6, it is very difficult oreven impossible to adjust writing parameters in the case where the wholeshape requires high dimension uniformity. In such case, the shape can beeither split in two (as illustrated in FIG. 6) if its intent categoryallows, or written by VSB method. In the latter case, fracturing rulespertinent to the shape's intent category apply.

EXAMPLE 4

If a CP cell candidate contains a dense line and space pattern asillustrated in FIG. 7, its image can be significantly distorted becauseof the Coulomb effect, as current density in this case is relativelyhigh. If the pattern's design intent dictates high writing accuracy, itis better to separate the pattern into two (as shown in FIG. 7) or evenmore patterns to minimize the distortions.

EXAMPLE 5

It is possible to prevent certain shapes from being placed in a CP cellby putting such shapes in a pertinent intent category and designing thecorresponding processing rules. Using the same method, one can forcecertain shapes to be placed in a CP cell.

EXAMPLE 6

Partial exposure of CP cells is a prominent extension of the technology.It allows writing of more patterns in one shot than the number of CPcells placed on a stencil mask. This method can be effectively used, forexample, for via layers. In via layers, via arrays of various size oftenoccur. In many cases, there are arrays with different size but equalpitch between elements. For that case, an array having maximum sizeallowable by stencil design rules can be use as a generic one-shotpattern. All arrays having equal or smaller dimensions, equal elementsize and equal pitch between elements can be written by one partialexposure of that generic element. Therefore, the number of CP cellsrequired to write a plurality of patterns can be reduced to one. Thesame considerations apply for other layers as well. FIG. 8 illustratesthe method for via and wire layers.

However, to expose a part of a CP cell, there should be a blank regionaround the cell that blocks the rest of the beam. If another CP cellappears in this region, a part of it will be exposed, as illustrated onFIG. 9. In this case, as depicted in (2 b) illumination region of FIG.9, two CP cells are illuminated by the beam. Therefore, in one approachfor implementing partial CP exposure, the cells are less densely packedthan those could be without using partial CP exposure.

To overcome this disadvantage, one approach is to use the cells that aresurrounded by the blank region that is used for VSB exposure. Howeverthe conventional method that uses the blank region consumes expensivestencil area. By this invention the periphery of the stencil (indicatedas space between apertures in FIG. 10) is used for the blank region andsaves waste of the stencil area. As beam distortion is higher on theperiphery, the periphery cells can be used as partial CP cells fornon-critical parts of the layout, while those cells that are surroundedby the blank area in the center of the stencil can be used as partial CPcells for critical parts of the layout. The position of such cells isdefined during the step 4 (308), taking the design intent into account.

EXAMPLE 7

To process data more effectively and faster and simultaneously providegood writing quality, in some approaches a configuration is establishedin which critical and non-critical patterns are not combined on one CPcell.

Illustrative Examples for Step 4 (308)

A method of achieving the goal of step 4 (308) according to someembodiments will be described and illustrated by considering thefollowing examples.

EXAMPLE 1

One can force certain CP cells to be placed on a stencil by assigning tosuch a category corresponding processing rules.

EXAMPLE 2

By assigning pertinent processing rules, CP cells that contain certainshape categories may be given higher (or lower) priority of placing onthe stencil.

EXAMPLE 3

CP cells placed on different positions of a stencil are written withdifferent accuracy. An accuracy map can be prepared that representswriting accuracy with respect to position on a stencil. For example,images of CP cells located closer to the optical axis of a writingmachine are usually less distorted (are written with higher accuracy)than those located closer to the periphery. In this case, one can buildan accuracy map as illustrated on FIG. 11. CP cells with the designintent that assumes higher quality can be placed in high accuracyregions. It can be easily done by assigning the corresponding processingrules to the corresponding intent categories.

Illustrative Examples for Step 5 (310)

A method of achieving the goal of step 5 (310) according to someembodiments will be described and illustrated by considering thefollowing example:

EXAMPLE

Assume that a shape with critical size is to be written using VSBmethod. To minimize Coulomb effect, the part of the shape adjacent toits boundary has to be fractured separately, and exposure dose for eachshape thus obtained has to be accurately calculated to minimizeproximity effects caused by the features lying in the shape's proximityregion. Even during the shot number estimation, it is necessary to takesuch fine fracturing into account to obtain an accurate shot numberestimate. This can be achieved by putting the shape into a pertinentintent category, and by assigning to this category the correspondingfracturing rules. The systems takes these rules into account whenestimating the number of shots for that shape.

ALTERNATIVE EMBODIMENTS

Most modem writing systems perform certain data processing operations(certain corrections etc) internally, just before actual writing of afeature, to increase writing quality and avoid unnecessary data volumegrowth. Such operations, however, are done uniformly, as the systemreceives only geometric information. In many cases, this leads either tounnecessary enhancements and longer writing time, or to shorter writingtime but lower overall quality.

The design intent information provided to the writing system along withgeometric data in a simple form suitable for fast real-time processingwill help to balance the speed and quality optimally. In this case theadditional work will be done only where necessary and to necessaryextent.

Although the proposed method is described in terms of processespertinent to IC fabrication, namely, Electron Beam Direct Writing andElectron Beam Mask Writing, the same approach can be used in any otherprocess of transferring images by means of controllable beam projectionequipment that uses VSB and CP techniques.

The same approach of separating the design into intent categories andintroducing category specific processing rules can be applied also to amask data preparation, or any other data preparation system to performmore optimal operations at less time.

As noted above, a great advantage of the present approach is that ittakes design intent into consideration. In the conventional systems,design intent is neither provided nor used. The present inventionprovides a unified way to treat design intent for any type of design. Asthe result, a single system capable of the optimal stencil design can bebuilt. Not only throughput but other requirements such as quality may betaken into account for any design using the described method.

The proposed method is also highly practical. It can be easilyimplemented as CAD system or its part, and can be used in combinationwith the existing systems to enhance capabilities of those.

The partial exposure method extends the number of CP patterns beyond thenumber of patterns that can be placed on a stencil. This overcomes otherapproaches in which enough blank space must be provided around a partialCP cell to make partial exposure possible, which decreases the totalnumber of CP cells on the stencil. Embodiments of the present inventiondescribes a way to overcome the problem, since certain CP cells can beused for partial exposure without decrease of the total number of CPcells.

System Architectures Overview

FIG. 12 is a block diagram of an illustrative computing system 1400suitable for implementing an embodiment of the present invention.Computer system 1400 includes a bus 1406 or other communicationmechanism for communicating information, which interconnects subsystemsand devices, such as processor 1407, system memory 1408 (e.g., RAM),static storage device 1409 (e.g., ROM), disk drive 1410 (e.g., magneticor optical), communication interface 1414 (e.g., modem or ethernetcard), display 1411 (e.g., CRT or LCD), input device 1412 (e.g.,keyboard), and cursor control.

According to one embodiment of the invention, computer system 1400performs specific operations by processor 1407 executing one or moresequences of one or more instructions contained in system memory 1408.Such instructions may be read into system memory 1408 from anothercomputer readable/usable medium, such as static storage device 1409 ordisk drive 1410. In alternative embodiments, hard-wired circuitry may beused in place of or in combination with software instructions toimplement the invention. Thus, embodiments of the invention are notlimited to any specific combination of hardware circuitry and/orsoftware. In one embodiment, the term “logic” shall mean any combinationof software or hardware that is used to implement all or part of theinvention.

The term “computer readable medium” or “computer usable medium” as usedherein refers to any medium that participates in providing instructionsto processor 1407 for execution. Such a medium may take many forms,including but not limited to, non-volatile media, volatile media, andtransmission media. Non-volatile media includes, for example, optical ormagnetic disks, such as disk drive 1410. Volatile media includes dynamicmemory, such as system memory 1408. Transmission media includes coaxialcables, copper wire, and fiber optics, including wires that comprise bus1406. Transmission media can also take the form of acoustic or lightwaves, such as those generated during radio wave and infrared datacommunications.

Common forms of computer readable media includes, for example, floppydisk, flexible disk, hard disk, magnetic tape, any other magneticmedium, CD-ROM, any other optical medium, punch cards, paper tape, anyother physical medium with patterns of holes, RAM, PROM, EPROM,FLASH-EPROM, any other memory chip or cartridge, carrier wave, or anyother medium from which a computer can read.

In an embodiment of the invention, execution of the sequences ofinstructions to practice the invention is performed by a single computersystem 1400. According to other embodiments of the invention, two ormore computer systems 1400 coupled by communication link 1415 (e.g.,LAN, PTSN, or wireless network) may perform the sequence of instructionsrequired to practice the invention in coordination with one another.

Computer system 1400 may transmit and receive messages, data, andinstructions, including program, i.e., application code, throughcommunication link 1415 and communication interface 1414. Receivedprogram code may be executed by processor 1407 as it is received, and/orstored in disk drive 1410, or other non-volatile storage for laterexecution.

In the foregoing specification, the invention has been described withreference to specific embodiments thereof. It will, however, be evidentthat various modifications and changes may be made thereto withoutdeparting from the broader spirit and scope of the invention. Forexample, the above-described process flows are described with referenceto a particular ordering of process actions. However, the ordering ofmany of the described process actions may be changed without affectingthe scope or operation of the invention. The specification and drawingsare, accordingly, to be regarded in an illustrative rather thanrestrictive sense.

These and other embodiments of the present invention may be realized inaccordance with the above teachings and it should be evident thatvarious modifications and changes may be made to the above describedembodiments without departing from the broader spirit and scope of theinvention. The specification and drawings are, accordingly, to beregarded in an illustrative rather than restrictive sense and theinvention measured only in terms of the claims.

1. A method of electron beam writing comprising: receiving stencildesign data; receiving design intent data; receiving equipmentcapability data; combining the stencil data, the design intent data andthe equipment capability data; determining an optimal electron beamwriting pattern based on the combined stencil data, the design intentdata and the equipment capability data; and directing an electron beamin accordance with the optimal electron beam writing pattern.
 2. Themethod of claim 1, further comprising considering throughput along withother requirements including quality.
 3. The method of claim 1, whereinthe method of electron beam writing includes a partial exposure method.4. The method of claim 3, wherein the partial exposure method extends anumber of cell projection patterns beyond a number of patterns that areplaced on a stencil.
 5. The method of claim 3, wherein cell projectionpatterns are used for partial exposure without decrease of the totalnumber of cell projection patterns by using periphery of the stencil forblocking unnecessary part of the electron beam.
 6. The method of claim1, further comprising categorizing a design of cell projection patternsby abstract intent categories and using one or more processing rules foreach category for designing a throughput and quality balanced stencil.7. A method for electron beam writing, the method comprising: accessinginput data or information; statistically analyzing a cell layout patternby calculating a number of repetitions of at least one cell of the celllayout pattern; building cell projection candidates by analyzingstatistical information of the repetitive portions of the cell layoutpattern; placing the cell projection candidates on a stencil; estimatingthroughput of the cell projection candidates; and generating a stenciltable.
 8. The method of claim 7, wherein accessing input data orinformation includes accessing at least one of design intent data,stencil data and equipment capability data.
 9. The method of claim 7,wherein accessing the input data or information includes at least one ofassigning criticality levels to various portions of the design anddefining geometric tolerances to classes of geometric shapes.
 10. Themethod of claim 7, wherein statistically analyzing a cell layout patternincludes determining the number of electron beam shots required to writethe cell layout pattern.
 11. The method of claim 7, wherein buildingcell projection candidates includes conforming repetitive portions ofthe cell layout pattern to one or more stencil design rules.
 12. Themethod of claim 11, wherein the one or more stencil design rules includeat least one of maximal size of cell, absence of forbidden patternsincluding donut shapes and cantilevers, shape density and shape sizeconstraints.
 13. The method of claim 11, wherein conforming repetitiveportions of the cell layout pattern to one or more stencil design rulesincludes modifying the cell layout pattern to conform to the one or morestencil rules.
 14. The method of claim 7, wherein estimating throughputof the cell projection candidates includes comparing the calculatedestimate against one or more corresponding targets.
 15. The method ofclaim 7, wherein estimating throughput of the cell projection candidatesincludes determining whether one or more predefined rules or conditionsare satisfied.
 16. The method of claim 7, wherein generating the stenciltable includes taping out the stencil data.
 17. A stencil design systemfor electron beam writing, the system comprising: at least one databasefor storing design intent data and stencil design rules; an electronbeam writer; and a processor for receiving design intent data andstencil design rules from the at least one database and for generating acell table for the electron beam writer.
 18. The system of claim 17,wherein the design intent data includes one or more cell layout patternsand the processor statistically analyzes each cell layout pattern bycalculating a number of repetitions of at least one cell of each celllayout pattern.
 19. The system of claim 18, wherein the processor buildscell projection candidates by analyzing statistical information of therepetitive portions of the cell layout pattern.
 20. The system of claim19, wherein the processor places the cell projection candidates on astencil.
 21. The system of claim 20, wherein the processor estimatesthroughput of the cell projection candidates.
 22. The system of claim17, wherein the cell table comprises a stencil table.
 23. A computerprogram product comprising a tangible computer usable medium havingexecutable code to execute a process for electron beam writing, theproduct comprising: a means to access input data or information; a meansto statistically analyze a cell layout pattern by calculating a numberof repetitions of at least one cell of the cell layout pattern; a meansto build cell projection candidates by analyzing statistical informationof the repetitive portions of the cell layout pattern; a means to placethe cell projection candidates on a stencil; a means to estimatethroughput of the cell projection candidates; and a means to generate astencil table.